We speak, metaphorically, of climbing mountains, but this graphic describes our climb using a simple staircase. It is our intention to move children forward - upward - on the staircase, and not to allow them to hesitate, vegetate, vacillate, or take root on a single step along the way. Hoggatteers also recognize that in a particular skill an individual may be at the top of the staircase, while s/he may be nearer the bottom when faced with a different standard. While it's not a great visual, we must imagine that we are climbing many cases of stairs simultaneously, and that others may perform better than I do at times, and yet I may perform better than they do at other times.
And that's OK!